Improving machinability of Inconel 718 with a new hybrid machining technique

In this paper, by joining three non-traditional machining methods — plasma-enhanced machining, cryogenic machining, and ultrasonic vibration assisted machining — a new hybrid machining technique for machining of Inconel 718 is presented. Cryogenic machining reduces the temperature in the cutting zone, and therefore decrease tool wear and increases tool life, while plasma-enhanced machining helps to increase the temperature in the workpiece to make it softer. Also, applying ultrasonic vibrations to the tool helps to improve cutting quality and to prolong tool life by lowering, mainly, the cutting force and improving the dynamic cutting stability. This study experimentally investigates the effect of cutting parameters on cutting performance in the machining of Inconel 718 and compares the results of hybrid machining and conventional machining (CM). It is found that the hybrid method results in better surface finish and improves tool life in hard cutting at low cutting speeds as compared to the CM method.     

Effect of cutting parameters on the degree of work hardening and tool life during high-speed machining of Inconel 718

The use of superalloy Inconel 718 is increasing in most of the sophisticated applications like aircraft engines, industrial gas turbines, rocket engines, space vehicles, submarines, etc. Hence, in-depth understanding of this material helps to determine the ability of this material to withstand severe conditions of stress, temperature, corrosion, and controls its longevity and reliability. In the present work, an attempt has been made to study the relationship of degree of work hardening and tool life as a function of cutting parameters like cutting speed, feed, depth of cut, untreated tungsten carbide and postcryogenic-treated tool. Work hardening and tool life are the major factors which need to be controlled/improved to enhance the machinability characteristics of superalloy Inconel 718. A significant performance in tool life was observed due to cryogenic treatment given to tungsten carbide tool. Moreover, it was observed that optimized cutting parameters not only minimized/controlled work hardening characteristics but also improved tool life while high-speed machining of Inconel 718.     

Study of surface quality in machining nickel-based alloy Inconel 718

In machining operation, the surface quality is one of the most important requirements for many workpieces. Because of the special physical and chemical properties, good-machined surface quality becomes a key issue to solve in machining Inconel 718. In this paper, PVD-TiAlN-coated carbide tools were used to turn Inconel 718. Based on observing the tool wear and machined surface morphology, the main factors affecting surface quality at different cutting speeds were analyzed. The optimal cutting temperature was calculated, according to the above analysis and Archard adhesion wear model, and further cutting parameters optimization was conducted, on the basis of the proposed optimal cutting temperature. The optimized cutting parameters based on optimal cutting temperature can be considered to improve surface quality.     

Chip Formation Mechanism of Inconel 718:A Review of Models and Approaches

Inconel 718,a nickel,chrome and iron alloy,has special advantages,such as high-temperature strength,thermal resistance and corrosion resistance,which facilitate wide usage in the aerospace industry,especially in the hot sec-tions of gas turbine engines.However,machining this alloy is correlated closely with the material's inherent properties such as excellent combination of strength,hardness and toughness,low thermal conductivity and the tendency to adhere to cutting tools.This nickel alloy also contains inclusions of hard abrasive carbide particles that lead to work-hardening of the workpiece material and thus abrasive wear of the cutting tool.That is,the machining of Inconel 718 is always influenced by high mechanical and thermal loads.This article reviews the chip formation mechanism of Inconel 718.One of the main characteristics in machining of Inconel 718 is that it will produce serrated or segmented chips in a wide range of cutting speeds and feeds.Existing studies show that the chip serration or segmentation by shear localization affects the machined surface integrity,and also contributes to the chip's evacuation and the auto-mation of machining operations.Thus,research conclusion indicates that the serrated or segmented chip phenom-enon is desirable in reducing the level of cutting force,and detailed analysis of models and approaches to understand the chip formation mechanism of Inconel 718 is vital for machining this alloy effectively and efficiently.Therefore,this article presents some summaries on the models and approaches on the chip formation in machining of Inconel 718.     

Intelligent optimization and selection of machining parameters in finish turning and facing of Inconel 718

The heat-resistant super alloy material like Inconel 718 machining is an inevitable and challenging task even in modern manufacturing processes. This paper describes the genetic algorithm coupled with artificial neural network (ANN) as an intelligent optimization technique for machining parameters optimization of Inconel 718. The machining experiments were conducted based on the design of experiments full-factorial type by varying the cutting speed, feed, and depth of cut as machining parameters against the responses of flank wear and surface roughness. The combined effects of cutting speed, feed, and depth of cut on the performance measures of surface roughness and flank wear were investigated by the analysis of variance. Using these experimental data, the mathematical model and ANN model were developed for constraints and fitness function evaluation in the intelligent optimization process. The optimization results were plotted as Pareto optimal front. Optimal machining parameters were obtained from the Pareto front graph. The confirmation experiments were conducted for the optimal machining parameters, and the betterment has been proved.     

Investigation of surface integrity in dry machining of Inconel 718

Machining of advanced aerospace materials have grown in the recent years although the diffucult-to-machine characteristics of alloys like titanium or nickel-based alloys cause higher cutting forces, rapid tool wear, and more heat generation. Therefore, machining with the use of cooling lubricants is usually carried out. To reduce the production costs and to make the processes environmentally safe, the goal is to move toward dry cutting by eliminating cutting fluids. This objective can be achieved by using coated tool, by increasing cutting speed, and by improving the product performance in term of surface integrity and product quality. The paper addresses the effects of cutting speed and feed on the surface integrity during dry machining of Inconel 718 alloy using coated tools. In particular, the influence of the cutting conditions on surface roughness, affected layer, microhardness, grain size, and microstructural alteration was investigated. Results show that cutting conditions have a significant effect on the parameters related to the surface integrity of the product affecting its overall performance.     

Development of a novel cubic boron nitride cutting tool with a textured flank face for high-speed machining of Inconel 718

Nickel-based superalloys such as Inconel 718 offer several advantages, including high-temperature strength and high corrosion resistance; this has led to a rapid increase in the demand for such materials, particularly in the aircraft industry. In contrast, these alloys are known to be among the most difficult-to-cut materials because of their mechanical and chemical properties, and tools used for this purpose have extremely short lifetimes. Recently, cubic boron nitride (CBN), which is the second hardest of all known materials, has received significant attention as a material for cutting tools and has already established itself in many fields of application. However, the performance of CBN tools is still insufficient for practical use, especially in the high-speed machining of Inconel 718. To overcome this problem, we first conducted orthogonal cutting experiments on Inconel 718 and performed cross-sectional observations of the CBN cutting tool in order to identify its wear mechanisms in continuous cutting operations under high-speed machining conditions (300 m/min). As a result, it was found that fatal tool failure occurs through crater and flank wear because of diffusion led by high cutting temperatures and subsequent chip adhesion to the tool flank face, accompanied by cutting edge chipping. Based on these results, a CBN cutting tool with a textured flank face was newly developed to improve the cutting tool life. Experimental: results showed that micro grooves generated on the flank face significantly suppressed the cutting edge chipping and remarkably extended the lifetime of the CBN tool during high-speed machining of Inconel 718.     

Finish Machining of Nickel-Base Inconel 718 Alloy with Coated Carbide Tool under Conventional and High-Pressure Coolant Supplies

Single-point turning of Inconel 718 alloy with commercially available Physical Vapour Deposition (PVD)-coated carbide tools under conventional and high-pressure coolant supplies up to 20.3 MPa was carried out. Tool life, surface roughness (Ra), tool wear, and component forces were recorded and analyzed. The test results show that acceptable surface finish and improved tool life can be achieved when machining Inconel 718 with high coolant pressures. The highest improvement in tool life (349%) was achieved when machining with 11 MPa coolant supply pressure at higher speed conditions of 60 m · min^?1. Machining with coolant pressures in excess of 11 MPa at cutting speeds up to 40 m · min^?1 lowered tool life more than when machining under conventional coolant flow at a feed rate of 0.1 mm · rev^?1. This suggests that there is a critical coolant pressure under which the cutting tools performed better under high-pressure coolant supplies.

Cutting forces increased with increasing cutting speed due probably to reactive forces introduced by the high-pressure coolant jet. Tool wear/wear rate increased gradually with prolonged machining with high coolant pressures due to improved coolant access to the cutting interface, hence lowering cutting temperature. Nose wear was the dominant tool failure mode when machining with coated carbide tools due probably to a reduction in the chip-tool and tool-workpiece contact length/area.     

Investigation and optimization of lubrication parameters in high speed turning of superalloy Inconel 718

Dry machining is sometimes less effective when higher machining efficiency, better surface finish quality, and severe cutting conditions are required. For these situations, semi-dry operations utilizing very small amount of cutting fluids called minimum quantity lubrication is expected to become a powerful tool and played a significant role in a number of practical applications. It has been observed from the literature survey that a systematic research work has to be carried out to determine the optimum quantity of lubricant with appropriate cutting conditions for achieving better machinability characteristics of a material. Hence, an attempt has been made in this paper to enhance the machinability characteristics in high speed turning of superalloy Inconel 718 using quantity of lubricant, delivery pressure at the nozzle, frequency of pulses, direction of application of cutting fluid, cutting speed, and feed rate as the process parameters. Results indicated that the use of optimized minimum quantity lubrication parameters under pulsed jet mode leads to lower cutting force, cutting temperature, and flank wear.     

Evaluation of machinability and economic performance in cryogenic-assisted hard turning of α-β titanium: a step towards sustainable manufacturing

Abstract

Titanium, a difficult-to-cut material, consumes higher time and cost in removing material by machining to produce parts. Machining of Ti alloys has got serious attention owing to its reactive nature with tool materials at elevated temperature that aggravates tool wear. Reportedly, effective and efficient cooling and lubrication at the tool–work interface can ameliorate the machinability of Ti-alloys. In this perspective, this article interrogates the underlying mechanism of critical responses such as surface roughness, temperature, tool life and machining cost under dry, minimum quantity lubrication (MQL) and cryogenic liquid nitrogen (LN2) modes. The effect of cutting speeds and feed rates on such responses have been considered as a function of cooling strategy to standardize the cooling technique as the best alternative for machining. Cryogenic cooling seems to be preponderant regarding machining cost, temperature, surface roughness and tool life in hard turning of a–b titanium alloy. The feasibility of cryogenic cooling was investigated using the iso-response technique in comparison with dry and MQL-assisted hard turning. Experimental results revealed longer tool life and lower machining cost under cryogenic condition followed by MQL and dry machining. Moreover, cryogenic LN2 has been identified as an appropriate alternative to reduce the temperature and surface roughness. On contrary, dry turning evoked a high-temperature and rapid tool wear. In a nutshell, cryogenic assisted hard turning has acceded as a sustainable strategy from an environmental and economic perspective.     

The performance Of DLC-coated and uncoated ultra-fine carbide tools in micromilling of Inconel 718

Coating is an important factor that affects cutting-tool performance. In particular, it directly affects surface quality and burr formation in the micro milling process. After the micromechanical machining process, surface quality is very hard to increase by a second process (grinding, etc.). In addition, in micromechanical machining, the cutting tool needs to have a good resistance to wear, owing to the fact that the cutting process is carried out at high speed. In this study, the machinability of Inconel 718 superalloy was investigated, using a Diamond Like Carbon (DLC) coated tool. The experimental tests were carried out in dry cutting conditions for different feed rates and depth of cuts. It was found that the dominant wear mechanism for all cutting parameters was identified to be abrasive and diffusive wear. Besides, a significantly Built Up Edge (BUE) formation was observed in uncoated tool. The results clearly show that DLC coating significantly decreased BUE. In addition, a smaller cutting force and better surface roughness were obtained with a DLC-coated tool. In conclusion, DLC coating can be used in micro milling of Inconel 718. It reduces the BUE and burr formation, improves surface roughness.     

Study of surface quality in high speed turning of Inconel 718 with uncoated and coated CBN tools

Inconel 718 is known to be among the most difficult-to-machine materials due to its special properties which cause the short tool life and severe surface damages. The properties, which are responsible for poor machinability, include rapid work hardening during machining; tendency to weld with the tool material at high temperature generated during machining; the tendency to form a built-up edge during machining; and the presence of hard carbides, such as titanium carbide and niobium carbide, in their microstructure. Conventional method of machining Inconel 718 with cemented carbide tool restricts the cutting speed to a maximum 30?m/min due to the lower hot hardness of carbide tool, high temperature strength and low thermal conductivity of Inconel 718. The introduction of new coated carbide tools has increased cutting speed to 100?m/min; nevertheless, the time required to machine this alloy is still considerably high. High speed machining using advanced tool material, such as CBN, is one possible alternative for improving the productivity of this material due to its higher hot hardness in comparison with carbide tool. This paper specifically deals with surface quality generated under high speed finishing turning conditions on age-hardened Inconel 718 with focus on surface roughness, metallographic analysis of surface layer and surface damages produced by machining. Both coated and uncoated CBN tools were used in the tests, and a comparison between surfaces generated by both tools was also discussed.     

Suppression of notch wear of a whisker reinforced ceramic tool in air-jet-assisted high-speed machining of Inconel 718

This paper describes the notch and flank wear specific to a SiC whisker reinforced alumina tool in air jet assisted (AJA) turning of nickel-base superalloy Inconel 718 at high cutting speeds. An AJA machining experiment has revealed that the air jet applied to the tool tip in addition to coolant dramatically reduces the depth-of-cut notch wear. As a result, the width of flank wear, but not the size of notch wear, determined the life of a ceramic tool in AJA machining of Inconel 718. This is a reason for the large extension and small variation of the tool life when high speed AJA machining is adopted. The maximum tool life length reached 2160 m at a cutting speed of 660 m/min under the given cutting conditions. Finally, the mechanisms of the notch and flank wear of a SiC whisker reinforced alumina tool in AJA machining are discussed from the viewpoints of tribochemical reactions and tool wear anisotropy.     

Tool wear and cutting forces under cryogenic machining of titanium alloy (Ti17)

Titanium alloy is well known for its difficulty to machine, owing to the important “tool wear” phenomenon. Machining assistance is an interesting solution to lengthen the tool lifetime. In this study, we focused on the effect of cryogenic assistance—during machining of Ti17—on the tool wear and cutting forces for different combinations of cutting speed, feed rate and depth of cut. Compared to conventional lubrication, cryogenic support lengthens the tool life for all tested conditions and has no significant influence on cutting force. A comparison of the cryogenic effect and high-pressure water jet assistance is also presented.     

Improving surface integrity in finish machining of Inconel 718 alloy using intelligent systems

In machining of hard materials, surface integrity is one of the major customer requirements which comprise the study of the changes induced to the workpiece. Surface roughness and residual stress are often considered as the most significant indications of surface integrity. Inducing tensile residual stress during the machining processes is a critical problem which should be avoided or minimized to obtain better service quality and component life. This problem becomes more evident in the presence of rough machined surface because fatigue life of manufactured components might be decreased significantly. Inconel 718 superalloy is one of the hard materials used extensively in the aerospace industries. It is prone to tensile residual stress in machined surface. Thus, controlling and optimizing residual stress and surface roughness in machining of Inconel 718 are so needed. Intelligent techniques based on the predictive and optimization models can be used efficiently for this purpose. In this study, the optimal machining parameters including cutting speed, depth of cut, and feed rate were accessed by intelligent systems to evaluate the state of residual stress and surface roughness in finish turning of Inconel 718. The results of experiments and analyses indicated that implemented techniques in this work provided a robust framework for improving surface integrity in machining of Inconel 718 alloy. It was shown that cutting speed has more effect on surface integrity than other investigated parameters. Also, depth of cut and feed rate were found in the moderate range to obtain satisfactory state of tensile residual stress and surface roughness.     

Cryogenic minimum quantity lubrication machining: from mechanism to application

Cutting fluid plays a cooling–lubrication role in the cutting of metal materials. However, the substantial usage of cutting fluid in traditional flood machining seriously pollutes the environment and threatens the health of workers. Environmental machining technologies, such as dry cutting, minimum quantity lubrication (MQL), and cryogenic cooling technology, have been used as substitute for flood machining. However, the insufficient cooling capacity of MQL with normal-temperature compressed gas and the lack of lubricating performance of cryogenic cooling technology limit their industrial application. The technical bottleneck of mechanical–thermal damage of difficult-to-cut materials in aerospace and other fields can be solved by combining cryogenic medium and MQL. The latest progress of cryogenic minimum quantity lubrication (CMQL) technology is reviewed in this paper, and the key scientific issues in the research achievements of CMQL are clarified. First, the application forms and process characteristics of CMQL devices in turning, milling, and grinding are systematically summarized from traditional settings to innovative design. Second, the cooling–lubrication mechanism of CMQL and its influence mechanism on material hardness, cutting force, tool wear, and workpiece surface quality in cutting are extensively revealed. The effects of CMQL are systematically analyzed based on its mechanism and application form. Results show that the application effect of CMQL is better than that of cryogenic technology or MQL alone. Finally, the prospect, which provides basis and support for engineering application and development of CMQL technology, is introduced considering the limitations of CMQL.     

Analysis of tool wear patterns in finishing turning of Inconel 718

This paper focuses on the analysis of tool wear mechanisms in finishing turning of Inconel 718, one of the most used Ni alloys, both in wet and dry cutting. Cemented carbides, ceramics and CBN tools are suitable for machining Ni alloys; coated carbide tools are competitive for machining operations of Ni alloys and widely used in industry. Commercial coated carbide tools (multilayer coating TiAl/TiAlN recommended for machining Ni alloys) were studied in this work. The feasibility of two inserts tested for dry cutting of Inconel 718 has been shown in the work. Experimental test were performed in order to analyze wear patterns evolution. It was found great influence of side cutting edge angle in tool wear mode.     

Modeling and experimentation on multistage work-hardening mechanism in machining with nose-radiused tools and its influence on machined subsurface quality and tool wear

The paper reports on the modeling and respective experimental validation for the formation of the machined subsurface layer in turning with nose-radiused and round tools. An experimental work on the mechanisms of work-hardening of the machined surface and related wear of the cutting tools was conducted for high-speed turning of aged Inconel 718 with whisker-reinforced alumina tools. The model shows that multiple deformations of the machined surface occur when machining with small feeds and tools with large nose radius, thus changing the mechanics of surface formation. Experimental results confirm the localized increase in subsurface hardness in the vicinity of the tool tip. The variation in the degree of work-hardening and the extent of the area affected by it fully agree with the predictions of the model. The model also shows that a significant part of the cutting tool may cut through the extra work-hardened material. Tool wear tests show that the local increase in workpiece hardness results in a localized increase in the wear rate of the cutting tools.     

A method of using Hoelder exponents to monitor tool-edge wear in high-speed finish machining

Tool condition monitoring is increasingly important as a widespread application of automated, computer numerically controlled machining in a variety of modern industries. Although a significant amount of research on tool condition monitoring in machining has been conducted during the past few decades, the research is primarily focused on tool flank wear. Less attention is paid to tool-edge wear, which is a critical issue in high-speed finish machining where the feed rate is in the same magnitude as tool edge dimensions, and thus, the tool cutting edge is subjected to extensive mechanical and thermal deformation. The present study fills this important research gap in tool condition monitoring. This paper presents a method of monitoring tool-edge wear in the high-speed finish machining of an aerospace superalloy Inconel 718 by extracting Hoelder exponents from wavelet transform analysis of cutting vibrations. A total of 60 cutting experiments were conducted, covering a range of cutting speed and feed rate conditions. The experimental results show that cutting vibrations increase as tool-edge wear develops. Wavelet transform analysis can be employed to identify single local maxima of the cutting vibration signals. As tool-edge wear develops, the values of Hoelder exponents vary from 0.55 to 0.90. It is suggested that under the cutting conditions tested in the present study, 0.8 can be used as the threshold value of Hoelder exponents to differentiate severe and normal tool-edge wear.     

Wear behavior and mechanisms of alumina-based ceramic tools in machining of ferrous and non-ferrous alloys

In this paper, the machining performance and wear mechanisms of two alumina-based ceramic cutting tools (Al₂O₃/TiB₂ and Al₂O₃/TiB₂/SiC_w) in continuous turning of hardened steel and nickel based alloy (Inconel 718) were examined. Results showed that in turning of hardened steel performed under identical conditions, Al₂O₃/TiB₂/SiC_w tool exhibited lower flank wear resistance than that of Al₂O₃/TiB₂ tool, the mechanisms responsible for this were determined to be the strong atom bonding between SiC and Fe, and the whisker pullout from the matrix for Al₂O₃/TiB₂/SiC_w ceramic tool. In continuous turning of Inconel 718, the Al₂O₃/TiB₂/SiC_w tool showed greatly improved flank wear resistance compared to Al₂O₃/TiB₂ tool, adhesion and abrasion wear were found to be the dominant wear mechanisms, the adhesion and diffusion of Ni, and Cr of Inconel 718 to the tool rake face may accelerate the tool wear rates.